This invention relates to sensing the concentration of glucose in biological fluids.
It is desirable to monitor accurately glucose concentration in biological fluids, particularly using a device that is implantable in living organisms; for example, such a device would be useful for diabetics in timing the administration of insulin and food.
Glucose concentration in simple solutions--e.g., Krebs-Ringer buffer--can be monitored electrochemically by measuring the current density at a platinum electrode while varying the electrode potential relative to a standard. At various electrode potentials, current generated by electrochemical reactions is responsive to the glucose concentration. Accordingly, current measured while varying the electrode potential over a range, first from negative to positive (anodic) and then back again (cathodic), will be a function of glucose concentration.* FNT *Marincic et al., "Electrochemical Glucose Oxidation on a Platinized Platinum Electrode in Krebs-Ringer Solution, I. Potentiodynamic Studies," 126 J. Electrochem. Soc. 43, January 1979 and "III. Effect of Urea," 126 J. Electrochem. Soc. October 1979.
Interference with glucose measurement due to the presence of other biological substances--particularly amino acids and urea--is a serious problem. Such substances undergo electrochemical reactions during the voltage sweep, generating currents independent of glucose concentration and reducing sensitivity to glucose.
Marincic et al., infra, indicates that there is considerable sensitivity of current density to glucose concentration in the presence of urea with cathodic potential sweeps at potentials below about -100 mV; that article concludes, however, for anodic potential sweeps, that inhibition by urea precludes glucose concentration measurement.
Gebhart et al., "Development of an Implantable Electrocatalytic Glucose Sensor", 5 Bioelectrochemistry and Bioenergetics 607 (1978) indicates (FIG. 9) a correlation between glucose concentration in the presence of amino acids and charge produced at the electrode at a specific voltage; between periods of integration, voltage is shifted to a rejuvenation potential.